1. Field of the Invention
The invention relates to the automatic recognition of image areas on an image-bearing original and, more particularly, to the automatic location of areas of exposure on an original for the purpose of calibrating an image scanner.
2. Background Art
It is known to record specific patterns on film for subsequent recognition by devices that classify image data or archive data, e.g., for a database supporting storage on microfilm. For example, in U.S. Pat. Nos. 4,691,112 and 4,283,621 a microfilm information system uses "blip" marks on a film support to locate microfilm document images for subsequent processing, e.g., such as archival and retrieval by a data processing system. Such "blip" marks can be shaped longer than average, as disclosed in U.S. Pat. No. 3,981,582, to form a command signal causing the system to undertake some function, e.g., to cut the film. Similarly, as disclosed in U.S. Pat. No. 4,777,515, the mark may have a length which corresponds to the size of the original that it references.
U.S. Pat. No. 3,266,393 describes a method for impinging, with accuracy, marks on film which would aid in the secondary appraisal of the exposure area of interest. The utility of this method includes the evaluation of aircraft reconnaisance photographs and applications related to photographic mapping. Another patent, U.S. Pat. No. 4,583,831, describes a technique for providing evenly spaced spot exposure of various code fiducials in binary form on a film. This would provide a means for further identification of an exposed area on the processed negative or positive. In the case where orientation of the image is important relative to its interpretation, U.S. Pat. No. 4,097,879 discloses a method of film exposure employing a mechanism within a camera body for indicating the top and bottom of the pictures -photographed, and accordingly exposing a U-shaped orientation mark on the film. The exposure information remaining in the field of view may then be interpreted as the top or bottom of the original scene depending upon the orientation of the U-shaped mark.
Generally, in the foregoing systems of the prior art, the exposure information contained in the overall image is not specifically used in operating the scanner. That is, once located, the exposure information will not be further utilized by the scanner itself, other than to properly categorize or direct the scanned information for subsequent processing. In photographic printing applications, as disclosed in U.S. Pat. No. 4,211,558, it is known to expose a density wedge nearby the image and then have the printer use the wedge for density and/or color corrections. However, in the '558 patent, no effort is made to precisely register the wedge. In electronic systems where certain exposure information is used by the scanner device itself, e.g., to calibrate its scanning components, it is imperative that the exposure information be accurately located and accurately detected. Particularly where the exposure information comprises many individual "patches" of separate information, and the input information is subject to angular orientation and magnification errors, present registration techniques do not provide sufficient accuracy in the location of the image points corresponding to the exposure areas.